Especially in the field of recording and/or playback of audio signals on a record carrier, digital encoding techniques are now the focus of interest. This interest is aroused by endeavours to develop a recording/reproducing system which guarantees a very high quality of the audio signal. A system which is eminently suitable for this purpose employs a disk-shaped record carrier in which audio information is recorded in the form of an optically detectable relief structure, which can be read by means of a radiation beam focused at the record carrier. The signal recorded on the record carrier is then digitally coded, so that a very wide dynamic range and a very high signal-to-noise ratio can be obtained. Digital recording also commands great interest for magnetic recording purposes.
However, for an optimum use of the possibilities presented by digital coding techniques the digital coding system should meet a number of specific requirements.
The principal requirement is that the bandwidth of the digitally coded signal should be limited. When digitally coded signal is transmitted via a transmission channel the signal bandwidth should obviously be within the available bandwidth of the transmission channel. Of course, this is also valid when the digitally coded signal is recorded on a record carrier. Moreover, in the last-mentioned case the bandwidth of the digitally coded signal has direct consequences for the playing time attainable with the record carrier.
A second important requirement is that the coding system be self-clocking, in other words that a clock signal can be derived from the digitally coded signal, which clock signal is necessary for decoding the digital signal. However, this is possible only if it is guaranteed that the digital signal contains a signal transition at regular intervals, in other words if the distance between consecutive signal transitions is not too great.